1. Field of the Invention
The present invention relates to a pin-fitting structure of a base-mount type address unit of a fire sensor in which an address unit including a nonvolatile memory for address-setting purposes is releasable mounted on a sensor base.
2. Description of the Related Art
In a conventional fire sensor of a type which answers a present detection condition in response to polling from a control unit utilizing a sensor address, it is necessary that an inherent address should be set in the fire sensor itself. The setting of the address for the fire sensor is effected usually by means of a nonvolatile memory (e.g. EEPROM) provided on a circuit board housed in a sensor body. When an address-setting circuit is provided in the sensor body itself, predetermined address-setting is effected for each sensor, for example, at the time of shipping from a factory. Needless to say, the address-setting may be effected at an installation site after installation of the sensor. One example in which an EEPROM, storing address, is provided in a sensor body is disclosed in U.S. Pat. No. 4,658,243.
On the other hand, there is a method in which a sensor address is set in a sensor base. In such a case where an address-setting circuit is provided on the sensor base mounted on a ceiling or the like, it is not necessary to effect address-setting relative to a sensor body, and the common sensor body can be attached to the sensor base. In this case, for example, in the cleaning of the fire sensor which is effected periodically after installation, the sensor body is entirely removed from the sensor base, and is cleaned at a time, and then the sensor body is again attached to the sensor base. In such a case, there is an advantage that even if the sensor address has been determined, the sensor body can be again attached to the sensor base without paying any attention to the sensor address.
For example, EP 0362985 A1 and EP 0546401 A1 disclose the type of structure in which an address is set in a sensor base, a sensor body is attached to the sensor base, and the address set in the sensor base is read to be stored in the body. However, in the address-setting system of EP 0362985 A1, a plurality of mechanical elements for indicating binary address codes are provided on the base, and switch elements for reading the address code by judging whether the mechanical elements are present or absent are provided on the body. Therefore, the number of the elements is large (If it is desired to set 255 addresses, eight elements are required), and there is a risk that incomplete contact may be encountered. Particularly when the base is mounted on a warped ceiling surface, the elements are not disposed horizontally, so that the risk of incomplete contact is further increased. In the address-setting system of EP 0546401 A1, an EEPROM storing address codes is provided on the base, and when the body is attached to the base, the address code is read from the EEPROM. However, in this publication, there is no mention of a structure of fitting between an ID module having the EEPROM and the body. On the other hand, even in the same fire sensor, the structure of the base differs depending on whether the address setting is made in the sensor body or the sensor base, and to design and manufacture such structures independently increases the cost. Therefore, it is preferred to prepare address units which can be releasably attached to the sensor base, in which case a necessary one of the address units is selectively attached to the sensor base.
However, in the structure in which the address unit is to be attached to the sensor base, a problem arises as to how the structure of connection between the address unit (particularly of the type including a nonvolatile memory such as EEPROM) and the sensor body is designed. Namely, the fire sensor is usually provided with a fitting structure by which the sensor body is rotated to be fitted relative to the sensor base to thereby connect them together mechanically and electrically. Usually, this fitting is achieved through two remote terminals. In the type having movable terminals, the fitting is effected through three terminals.
On the other hand, the address unit incorporated in the sensor base requires a power line, signal lines for clock purposes and read-write purposes. Accordingly, for example, the connection through four terminals is needed. Therefore, the total number of the terminals for the sensor body and the sensor base is 6 to 7, and the conventional rotation-fitting structure can not be employed because of an installation space.
Therefore, it may be proposed that instead of using the rotation-fitting structure for the address unit, the signal wires are extended long enough to be connected by a connector. However, in such a structure in which the signal lines are extended from the address unit or the sensor body into a length allowing the rotation-fitting, and are connected to the mating unit by the connector, the originally-intended function of directly fitting the sensor base and the sensor body together is lost, and it is difficult to put this structure into practical use.